Windows application. A program that is written to run under the Microsoft Windows operating system, also called a "Windows app." All 32-bit Windows applications run in the 32-bit and 64-bit versions of Windows. All 64-bit applications require 64-bit Windows, which is the standard on new Windows computers and tablets.
Microsoft Windows is an operating system. Its purpose is to access the hardware in your PC to provide an environment for applications to be run during a computer session. Windows in and of itself is not an application, but a collection of specialized program components.